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The Process of Osmosis and its Importance to Living Organisms.

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´╗┐The Process of Osmosis and its Importance to Living Organisms. Osmosis is the diffusion of water through a semipermeable membrane that does not allow dissolved solids (solutes) to pass. Osmosis refers only to diffusion of water and the direction of movement is from the area of higher concentration to the area of lower concentration. This migration of water from a region of higher concentration to a region of lower concentration is spontaneous and although water molecules move in both directions, the net movement is from a region of higher concentration to a region of lower concentration. Osmosis is of prime importance in living organisms, where it influences the distribution of nutrients and the release of metabolic waste products such as urea. Many nutrients and essential molecules that one needs to live are dissolved in water. So if water couldn't diffuse, we wouldn't get essential molecules to live. If blood cells, for example, are placed in contact with an isotonic solution, they will neither shrink nor swell. ...read more.


Urea is a small, uncharged molecule, so it can pass through membranes by lipid diffusion and there isn?t much the kidney can do about it. Since this is a passive process, urea diffuses down its concentration gradient until the concentrations of urea in the filtrate and blood are equal. So in each pass through the kidneys half the urea is removed from the blood and half remains in the blood. Many marine organisms are highly affected by changes in salinity. This is because of a process called osmosis which is the ability of water to move in and out of living cells, in response to a concentration of a dissolved material, until equilibrium is reached. In general the dissolved material does not easily cross the cell membrane so the water flows by osmosis to form equilibrium. Marine organisms respond to this as either being osmotic conformers (also called poikilosmotic) or osmotic regulators (or homeosmotic). Osmotic conformers have no mechanism to control osmosis and their cells are the same salt content as the liquid environment in which they are found. ...read more.


Special cells on the gills called chloride cells excrete the salt so the fish can replace its lost water. When a salmon migrates to fresh water its cells start to take on water so the salmon stops drinking and its kidneys start working to produce large amounts of urine to expel the water. Plants gain water through osmosis in their roots from the soil. Without a water potential gradient, water will be loss from the roots. Plant cells contain vacuoles, which, if not full with water, will cause the cell to become flaccid. If all the cells in a leaf become flaccid, the whole leaf will become flaccid, hence causing the plant to wilt. Plant cells therefore need water to remain turgid and keep firm. If an animal cell surrounded with a high water potential, osmosis will take place, and if the water is not expelled some way or another, the cell will burst. This is because an animal cell doesn?t have a cell wall to keep it strong. If an animal cell is surrounded with low water potential, the water in the cytoplasm will diffuse outwards, causing the cell to shrink. ...read more.

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